The present invention relates to resistance welding equipment, and more particularly to a portable meter for determining the impedance between two points of a resistance welding device.
In resistance welding, coalescence is produced primarily by resistive heat created by passing an electric current through the work-piece. A resistance welder includes primary conductors, a transformer, secondary conductors, and welding electrodes or tips. The primary conductors couple the transformer to a power source. The secondary conductors interconnect the transformer and the electrodes.
Manufacturers of resistance welding transformers are frequently required to specify a transformer required to weld two given pieces of material together. The choice of a transformer is determined by the secondary voltage required to drive the necessary weld current through the welding circuit. The required weld current, along with other data such as weld force, weld time, and the like, to make the weld can be determined from weld schedules published by the American Welding Society (AWS) and the Resistance Welding Manufacturers Association (RWMA). With the required weld current known, the impedance of the welding circuit must be determined to calculate the necessary voltage using Ohm's Law.
The impedance of the welding circuit is the geometric sum of all resistances and reactances in the welding circuit. Calculation of these values is difficult since conductor cross-sections, conductor materials, current path lengths, and the geometry of the weld circuits are not readily defined in mathematical terms. The measurement of impedance in resistance welding circuits has been practiced for many years but requires cumbersome equipment, extensive instrumentation, and in-depth knowledge of electrical engineering.